Many electrical devices such as motors are operated on a three phase electrical system. It is common to protect such devices with an overload relay which monitors current flowing in the three phase electrical system. When current supplied to the protected device is above a predetermined safe limit, the relay causes a contactor in series with the protected device to open. The loss of any one of the three phases of the electrical system can cause improper operation or significant damage to electrical the device. Therefore it is also desirable that the overload relay be capable of detecting a phase loss condition. A method of phase loss detection is disclosed by Reed et al. in U.S. Pat. No. 4,823,226, assigned to the present assignee and incorporated herein by reference. It is also known for the electrical phases to become unbalanced due to an overload or an underload condition in any one of the phases. The phase imbalance condition can have the same effect on electrical devices as the overload or phase loss conditions. Libert, in U.S. Pat. No. 4,724,503, assigned to the present assignee and incorporated herein by reference, discloses a method of phase loss and phase imbalance protection to be incorporated into a reduced voltage starter. The device of Libert senses the voltage waveform and compares the zero crossing point of each phase to determine phase loss and phase imbalance. The Libert device is a high end device which is significantly more complex than the current sensing low end device of Reed and thereby requires many more electrical components which increase the manufacturing cost. Any device such as Reed's which senses current flowing in the protected circuit is limited in its accuracy and ability to detect phase imbalance due to harmonically distorted current wave shapes which may be produced by starters such as a solid state reduced voltage starter running a motor in the economy mode. These harmonically distorted wave shapes appear to the overload relay as a phase loss condition and thereby cause nuisance tripping. In order to reduce the nuisance tripping, the percentage of imbalance allowed in such a system must be increased. This increases the chance that an overload or underload may be present in one phase of the system without causing the phase loss or unbalance detection circuits to initiate a trip condition. The National Electric Code 1993 (NEC) Article 430-34 Selection of Overload Relay requires that conductors supplying current to a motor be rated at 125% of the Motor Full Load Amperage (MFLA) per Articles 430-432 (a)(1) and (c)(1). Articles 430-434 also permit the current in the motor circuit to increase to 140% of MFLA during start up. It would therefore be desirable to have a phase unbalance detection circuit that is capable of detecting and initiating a trip when the phase unbalance in the system is greater 15% of the MFLA. It is also desirable to have this accurate phase unbalance detection circuit in a low end, low cost current sensing overload relay.